Various electron tubes have been proposed. The electron tubes have a photocathode that emits photoelectrons in response to an incident light and a detection section constituted by a semiconductor device or a multiple-stage dynode that amplifies the photoelectrons so as to detect them.
As an electron tube using a dynode, there is available an electron tube having substantially a spherical main body and a cylindrical base. In the electron tube, a photocathode is formed on the internal surface of the main body and a first-stage dynode is disposed on the main body side relative to the base (refer to, for example, Patent Document 1).
As an electron tube using an avalanche photodiode (hereinafter, referred to as APD) as the detection section, there has been proposed an electron tube in which an entrance window and a conductive stem are disposed opposite to each other at both ends of an insulating container; a photocathode is formed on the internal surface of the entrance window; and the APD is disposed on the conductive stem. The conductive stem protrudes in the direction toward the photocathode (refer to, for example, Patent Document 2).
As an electron tube using a semiconductor device as the detection section, there is also available an electron tube in which a photocathode is formed on the internal surface of a window with a curved surface having a center of curvature inside the electron tube, and a photodiode is disposed on the opposite side to the photocathode (refer, for example, to Patent Document 3).
[Patent Document 1]
Japanese Patent Application Laid-Open Publication No. 9-35680 (pages 3 to 5, FIG. 1)
[Patent Document 2]
Japanese Patent Application Laid-Open Publication No. 9-297055 (pages 4 to 9, FIG. 4)
[Patent Document 3]
Japanese Patent Application Laid-Open Publication No. 5-54849 (pages 2 to 4, FIG. 1)